Most traffic signals are illuminated by incandescent lamps that are threaded into standard electrical screw-in lamp sockets. The lamps have colored and/or masked lenses over them to indicate to drivers and pedestrians when they can enter the intersection. The masked lenses form symbols such as an arrow, a hand, a person walking, letters or even words by blocking light from passing through selected portions of the lenses.
Conventional illuminated traffic signals have several drawbacks. The standard incandescent lamps used therein have relatively short life spans. Further, such lamps consume significant amounts of energy. These problems are of special concern because most traffic signals operate continuously. Another drawback with conventional traffic signals is that the masked lenses used to create the illuminated symbol images waste energy because they block light produced by the lamp in order to form the images. Therefore, a significant amount of light from the lamps is wasted as heat absorbed by the lenses instead of light being projected out to the traffic.
There is a need for a traffic signal lamp that has a longer lifetime and uses less energy than conventional traffic signal lamps. Further, there is a need for such a lamp to form the necessary illuminated symbol images without having to use masked lenses that are expensive and waste energy. Lastly, there is a need for such a lamp to be compatible with the standard screw-in electrical lamp socket so that existing traffic signals can be retrofitted with the new lamp.